6. Work on your left-hand technique.
OK, you're working on your all-important right hand, but what about your left? (When it comes to the mandolin, if you follow the biblical injunction not to let your left hand know what your right hand is doing, you won't make a very joyful noise.) Here are a few ideas:
As you pick a tune, you should look at your left hand position very carefully. Are you lifting your fingers more than you need to? Every millimeter you pull your finger back after you hit a note is a millimeter you have to repeat on the way back, and the farther away you go, the more likely to mess up on return, and the slower you'll play overall. Speed is in your right hand, certainly, but it's also in your left fingers.
Check out the pressure of your fingers on the string. You need to press hard enough to make the note sound clearly, but anything over that is wasted effort, again slowing you down, as well as causing fatigue and worse. I have a bad tendency to squeeze too hard, especially when I try to play faster, and of course that only slows me down. It's good to be conscious of your left hand pressure.
Tunes and musical pieces (for you classical pickers!) are an endless source of left-hand workouts. When you find an interesting passage, you should isolate on it as practice. So if you hit a series of arpeggios that make you cross three strings, or you have a lick that makes you do something that really works your pinky, isolate on the passage and practice it not only for the tune itself, but also for technique in general.
Dan Crary suggests this method for learning the fingering of new tunes: press really hard as you play. The idea is that the extra pressure burns the notes in on your fingers and thus your brain. (Contradicts #2 above, but this is only for learning.)
You can figure out fingering exercises to work on each of your fingers, especially the pesky pinky. Here's one: start with your index finger on the 2nd fret of the G string, then play the 3rd fret (or 4th fret) with your middle finger. Then move to the D string (2nd and 3rd or 4th frets), then A, then E. You can repeat the two fingers on each string four or five times, then move to the next string (all this with a metronome, of course). Then play with index finger on second fret, ring finger on fifth or sixth, then index and pinky (on 7th or 8th fret). (Then middle finger and ring, etc.) This will really give all your fingers a good workout. You might also find some sounds you wouldn't otherwise hear (or never want to hear again!)
Whew, that confused ME, and I think I know what I meant! Any other left handed ideas?